1 / 23

Mendelian Genetics

Mendelian Genetics. Key Terms in Mendelian Genetics. Phenotype: observable traits Examples: brown eyes, yellow flower Genotype: actual alleles; describes the genetic characteristics The combination of alleles inherited Examples: BB, dd , Ff. Phenotype: brown eyes

osanna
Download Presentation

Mendelian Genetics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Mendelian Genetics

  2. Key Terms in Mendelian Genetics • Phenotype: observable traits • Examples: brown eyes, yellow flower • Genotype: actual alleles; describes the genetic characteristics • The combination of alleles inherited • Examples: BB, dd, Ff Phenotype: brown eyes This is the trait that is expressed! Genotype: could be BB or Bb This is the 2 alleles that were inherited from mother & father!

  3. Key Terms in Mendelian Genetics • Homozygous: having 2 identical alleles for a trait • TT or tt • “homo” means “same” • Heterozygous: having 2 different alleles for a trait • Tt • “hetero” means “different” Genotype: could be BB or Bb This person could be homozygous dominant (BB) or heterozygous (Bb) for the eye color trait!

  4. What color hair will Kate Middleton’s & Prince William’s baby have? • We can use our knowledge of genetics & meiosis to make a prediction!

  5. Meiosis • Remember! • During meiosis, our bodies make egg & sperm cells. • Egg & sperm cells contain ½ the amount of DNA as other cells. Why?

  6. What color hair will Kate Middleton’s & Prince William’s baby have? • We now know that Prince William can only pass on the “b” allele. • Kate can pass on a “B” or a “b” to the baby. • To make our prediction, we have to draw a Punnett Square!

  7. Punnett Squares • Diagrams we can draw to help us predict the genotypes & phenotypes of offspring

  8. Start with a blank box with 4 empty squares. Add the genotype of each parent to the top & left side of the box (outside). Father is on top & mother is on the left side. b b B b

  9. Fill in the squares! Remember that each parent only passes on 1 allele for the hair color gene! b b B Bb Bb bb bb b

  10. Remember, alleles are a version of a gene.

  11. What do the results of the Punnett square mean? Kate and William will have 4 children Two children will look like Kate, two will look like William There is chance that a baby will have brown hair, and a chance that it will have blonde hair

  12. B=brown, b=blonde What color hair will the offspring have if they inherit these alleles? Bb=?

  13. What are the chances that the baby will have blonde hair? 25% 75% 50% No chance 50%

  14. 3:1Phenotype = tall or shortThere’s a 75% chance the offspring will be tall & a 25% chance the offspring will be short! What’s the phenotypic ratio in the offspring? • 1:2:1 • 1:1:1:1 • 3:1 • What?!

  15. Mendelian inheritance reflects the rules of probability! • Mendel’s laws of segregation & independent assortment reflect the same laws of probability that apply to tossing coins or rolling dice. • The probability of tossing heads with a normal coin is 1/2.

  16. When tossing a coin, the outcome of 1 toss has no impact on the outcome of the next toss! • Each toss is an independent event, just like the distribution of alleles into gametes. Like a coin toss, each egg cell from a heterozygous parent has a ½ chance of carrying the dominant allele & ½ chance of carrying the recessive allele! (The same odds apply to sperm.)

  17. Law of Segregation This parent is carrying 2 alleles for a gene. Genotype = Ss During meiosis, the alleles are separated into 4 gametes. Each gamete has a 50% chance of carrying S & a 50% chance of carrying s.

  18. By the law of segregation, the 2 alleles for a gene are packaged into separate gametes. • Here, the F1 hybrids all have purple flowers.

  19. When Mendel crossed the F1 plants together, the F2 generation included both purple & white flowered plants! • The white flowered allele was absent in the F1 plants, but reappeared in the F2 plants! Based on a large sample size, Mendel recorded 705 purple plants & 224 white plants in the F2 generation. What’s the ratio of purple to white plants?

  20. Mendelian Ratios ¼ of the F2 offspring will inherit 2 white flower alleles & produce white flowers. (p + p = pp) ½ of the F2 offspring will inherit 1 white flower allele & 1 purple flower allele & produce purple flowers. (p + P = Pp) ¼ of the F2 offspring will inherit 2 purple flower alleles & produce purple flowers. (P + P = PP) This represents a 3:1 ratio in the F2 generation!

  21. What’s the phenotypic ratio for these offspring? • 1:2:1 • 3:1 • 2:1 • 1:1 1:1 Phenotype = yellow or green pea pod The chances of the pea pods being yellow are equal to them becoming green!

  22. The Genotypic Ratios 50% Yy 0% YY 50% yy

More Related